Exchange Rates, Currency Markets, and Why Currencies Rise or Fall
Every country has its own money. The moment a German buys a phone from Japan, or an Indian software firm sells to a US client, two different monies must meet and trade. The price at which they trade is the exchange rate. This chapter explains what that price is, why it moves, how the world's largest market sets it, and how whole nations have been broken when that price went wrong.
What an exchange rate actually is
An exchange rate is simply the price of one currency measured in another. If 1 US dollar (USD) buys 83 Indian rupees (INR), the rate is 83 INR/USD. That is all it is — a price, set where supply meets demand, exactly like the price of apples or oil.
- Appreciation
- A currency gets stronger — it buys more foreign money. If the rupee moves from 83 to 80 per dollar, the rupee appreciated (you need fewer rupees per dollar).
- Depreciation
- A currency gets weaker — it buys less. Rupee moving from 83 to 86 per dollar is depreciation.
- Devaluation / revaluation
- The deliberate policy versions, used when a government holds the rate fixed and then officially moves it. "Depreciation" is what the market does; "devaluation" is what a government chooses.
When you change money at a bank you meet two prices: the bid (what the dealer pays to buy your currency) and the ask (what it charges to sell you currency). The gap — the bid/ask spread — is the dealer's profit. A spot deal settles almost now (about two days); a forward locks in a rate today for delivery on a future date, which is how exporters protect themselves against the rate moving against them.
Floating vs fixed: who decides the rate?
There are two basic ways to run a currency, and the choice shapes a country's whole economy.
| Regime | Who sets the rate | Examples | Main risk |
|---|---|---|---|
| Floating | The market, freely | USD, EUR, GBP, JPY | Volatility — the rate can swing fast |
| Managed float | Mostly market, central bank nudges | Indian rupee, most large economies | Reserves spent smoothing moves |
| Fixed / pegged | Government commits to a level | Saudi riyal & UAE dirham (to USD), Danish krone (to EUR) | Peg can break if reserves run out |
To hold a peg, a central bank must stand ready to buy or sell its own currency using its stockpile of foreign exchange reserves (mostly held in dollars). The most rigid version is a currency board: every unit of local money issued is legally backed by an equivalent reserve. Hong Kong has run one since 1983, holding the Hong Kong dollar near 7.80 per USD for four decades.
But you cannot have everything. The impossible trinity (or trilemma) says a country can pick only two of these three: a fixed exchange rate, free movement of capital across borders, and an independent monetary policy (the ability to set its own interest rates). Hong Kong chose a fixed rate and free capital — so it gives up control of its own rates and effectively imports US monetary policy.
What makes a currency strong or weak
Six forces push the price up or down. Watch how each one becomes a chain of cause and effect.
- 1. Interest rates (the biggest driver)
- What matters is the real interest rate — the rate after subtracting inflation. When a central bank raises real rates, foreign investors chase the higher yield: they buy the currency to invest, demand rises, the currency appreciates. Cut rates, and money flows out, the currency falls.
- 2. Inflation
- Money that loses value at home loses value abroad. Persistently high inflation steadily erodes a currency (this is the deep logic behind PPP, below).
- 3. Trade balance
- Exporters earn foreign currency and sell it for home currency — that raises demand for the home currency. Importers do the reverse. Chronic trade deficits push a currency down... unless capital inflows offset them.
- 4. Capital flows
- Foreign investment — into shares, bonds, factories — creates demand for the currency. But fast-moving "hot money" can reverse overnight and trigger a crash.
- 5. Confidence and safe-haven status
- In a panic, money flees to the dollar, Swiss franc, and yen regardless of their fundamentals. This "flight to safety" can lift a currency even when its own economy is weak.
- 6. Central bank action
- Tightening (raising rates, shrinking the money supply) strengthens a currency; large-scale bond-buying (quantitative easing) weakens it.
WHAT MOVES A CURRENCY (demand vs supply for it) ┌──────────────────────────────────────────────────────┐ │ Higher real rates ─┐ │ │ Strong exports ────┤ │ │ Capital inflows ───┼──► DEMAND for currency ↑ ──► UP │ (appreciation) │ Safe-haven panic ──┘ │ │ │ │ High inflation ────┐ │ │ Trade deficit ─────┤ │ │ Capital flight ────┼──► SUPPLY of currency ↑ ──►DOWN │ (depreciation) │ Rate cuts / QE ────┘ │ └──────────────────────────────────────────────────────┘
How the foreign-exchange market works
The forex (FX) market is the largest, most liquid market on Earth. The Bank for International Settlements found roughly $7.5 trillion changed hands every single day in April 2022 — more in a day than many countries produce in a year. It has no central building. It is decentralized and over-the-counter (OTC), running 24 hours a day, five days a week, dominated by a handful of giant banks trading with each other (the "interbank" market).
The dollar sits on one side of about 88% of all trades — it is the world's plumbing. The euro (~31%), yen (~17%), pound (~13%) and a rising Chinese renminbi (~7%) follow.
The carry trade: picking up nickels in front of a steamroller
The carry trade is one of the most popular bets in finance. You borrow in a currency with very low interest rates and invest in one with high rates, pocketing the difference. The classic is the yen carry trade: borrow yen at near 0%, convert to dollars, buy US assets yielding 5–6%. As long as the yen stays cheap, you earn the gap for free.
The danger is that the funding currency suddenly rises — and then everyone rushes to unwind at once, selling their investments to repay loans that just got more expensive.
When currencies break: real crises
A peg is a promise, and markets test promises. When a fixed rate is set wrong, traders attack it, and a determined market beats a defended peg every time the fundamentals are misaligned.
Devaluation is not always failure. A weaker currency makes a country's exports cheaper and can restore competitiveness. Turkey shows the opposite extreme: an unorthodox policy of cutting rates to fight inflation helped the lira lose over 80% against the dollar from 2021–2024, with inflation still near 33%.
Why the same product costs different amounts: PPP revisited
Purchasing Power Parity (PPP) is the idea that, in theory, an exchange rate should equalize the price of the same good everywhere. In reality it doesn't, because much of life isn't tradable across borders — rent, haircuts, local labor — plus tariffs, transport, and taxes get in the way.
The Economist's playful Big Mac Index (since 1986) makes this vivid: compare the price of a Big Mac across countries. In July 2025 readings, a burger was far cheaper in Japan, implying the yen was about 41% undervalued versus the dollar, while the Swiss franc looked overvalued. It is illustrative, not gospel — a burger isn't shipped internationally — but it explains why your salary "goes further" in a low-cost country.
Key Takeaways
- An exchange rate is the price of one currency in another, set by supply and demand like any price.
- Floating rates move with the market; fixed/pegged rates are defended with reserves — and the trilemma forbids having a fixed rate, free capital, and independent policy all at once.
- The strongest single driver is the real interest-rate gap; inflation, trade balance, capital flows, and panic-driven safe-haven demand do the rest.
- Forex is a ~$7.5 trillion-a-day OTC market where the dollar sits on ~88% of trades (shares total 200% because each trade has two sides).
- The carry trade earns the rate gap until the funding currency spikes — then a synchronized unwind (August 2024) spreads losses globally.
- Misaligned pegs invite attack: Black Wednesday 1992 and the 1997 Asian crisis show a determined market beats a defended peg.
- PPP and the Big Mac Index explain why identical goods — and your salary — buy different amounts across countries.